I like variety - since I mainly DM I have this covered.

In terms of playing: well I like illusionists and skill monkeys which has pointed me at Beguiler.

I also have a fondness for Ranger type characters - though you can do a lot better, buildwise, than to use that class.

I quite like unusual cleric type characters. These are often the strongest in terms of role-play.

I also like multi-threat characters because they have more options.